1. Field of the Invention
The present invention relates to an arch clamp foot pressing device of a sewing machine, particularly to an arch clamp foot pressing device such as a bar tacking machine capable of performing automatic cycle sewing.
2. Prior Art
FIG. 15 is a schematic view of a conventional bar tacking machine comprising a workpiece clamping unit 30 which has a arch clamp frame 1 disposed on a bed 9, a workpiece clamping unit driving mechanism 40 which is disposed in the bed 9 and drives the workpiece clamping unit 30 in given directions, back and forth (right and left in FIG. 15) and right and left (vertical direction relative to the paper surface in FIG. 15), and a clamp lifting mechanism 17 which is disposed in an arm 16 for driving arch clamp feet 5 up and down. The clamp lifting mechanism 17 includes a solenoid actuator 34 having a plunger 34a, a guide bushing 36 attached to the arm 16, a pressing member 18 which has a flange 18a and the up and down movement thereof is guided by the guide bushing 36, and a transmitting mechanism 37 which transmits the protruding and entering operation of the plunger 34a of the solenoid actuator 34 to the pressing member 18 to cause the pressing member 18 to move up and down. The transmitting mechanism 37 comprises a pair of links which are connected to form a shape of angle, and the pressing member 18 is moved up and down by changing the amount of bending of a pair of links.
A pin 2 is fixed to the arch clamp frame 1 and an arch clamp foot lifting lever 3 is turnably supported by the pin 2. The arch clamp foot lifting lever 3 is always biased counterclockwise about the pin 2 serving as a fulcrum by an compression spring 4, and a tip end portion 3b is engaged in the arch clamp feet 5 which are disposed on the arch clamp frame 1 to move up and down. With the counterclockwise biasing of the turning of the arch clamp foot lifting lever 3 , the arch clamp feet 5 are lowered so that the workpiece is clamped on a feed plate 10. The feed plate 10 is formed integrally with the arch clamp frame 1.
In the bar tacking machine, the entering operation of the plunger 34a caused by energizing the solenoid of the solenoid actuator 34 lowers the pressing member 18 by way of the transmitting mechanism 37. Accordingly, a projection 15, and hence the base end portion of the arch clamp foot lifting lever 3 rather than the pin 2 is pressed downward by the flange 18a of the pressing member 18 so that the arch clamp foot lifting lever 3 is turned clockwise about the pin 2 against resiliency of the compression spring 4, and hence the arch clamp feet 5 move upward. With the upward movement of the arch clamp feet 5, a workpiece clamped between the arch clamp feet 5 and the feed plate 10 is released.
On the other hand, when the solenoid of the solenoid actuator 34 is deenergized, the pressing member 18 is moved upward by way of the transmitting mechanism 37. Consequently, the pressing member 18 comes into contact with the lower surface of the guide bushing 36 fixed to the arm 16, releasing the pressed state of the projection 15 of the pressing member 18. As a result, the arch clamp foot lifting lever 3 receiving the resiliency of the compression spring 4 is turned counterclockwise about the pin 2 to lower the arch clamp feet 5 so that the workpiece can be clamped between the arch clamp feet 5 and the feed plate 10.
The arch clamp frame 1 of the workpiece clamping unit 30 and the feed plate 10 are moved in given directions, back and forth and right and left on the upper surface of the bed 9 by the workpiece clamping unit driving mechanism 40 while the workpiece is clamped between the arch clamp feet 5 and feed plate 10, thereby subjecting the workpiece to a given bar tacking by a needle 41.
However, in the conventional arch clamp foot pressing device, the arch clamp feet 5 are vertically movably received in grooves 1b of the arch clamp frame 1 in the same manner as shown in FIG. 6 so that it is prevented from coming off by retaining plates 6. All the retaining plates 6 for retaining the arch clamp feet 5 from the outside are secured in given positions by set screws 8. Accordingly, when the arch clamp feet 5 are replaced with other to cope with the content of the sewing operation, all the set screws 8 fastening the retaining plates 6 are removed, then the arch clamp feet 5 are replaced with other, and thereafter the set screws 8 are again fastened, which are very troublesome. As a result, there occurs a problem that the replacing operation of the arch clamp feet 5 involved in the change of sewing operation in the sewing factory causes the deterioration of the rate of operation.